Tobacco use and alcohol consumption are the major risk factors for squamous cell carcinoma of the head and neck (SCCHN). However, only a fraction of smokers develop SCCHN, which suggests that subgroups of the general population are genetically susceptible to SCCHN. We hypothesize that genetic susceptibility plays a role in the etiology of SCCHN and that there is an interaction between genetic susceptibility and exposure to tobacco and alcohol. To test this hypothesis, we propose to conduct a molecular epidemiological case-control study (800 cases and 800 controls) to investigate the associations between selected phenotypic and genotypic markers of genetic susceptibility and risk of developing SCCHN and search for potential gene-environment interactions in SCCHN. Our specific aims are: Aim 1: To construct a comprehensive epidemiological and clinical database. Cases will be newly diagnosed SCCHN patients at M. D. Anderson Cancer Center and controls will be age-, sex-, and ethnicity-matched healthy subjects identified from genetically unrelated hospital visitor controls. Aim 2: To determine the main effects of the selected biomarkers for genetic susceptibility on risk of SCCHN, a panel of well-developed in vitro functional assays is proposed: A. Phenotypic DNA repair capacity (DRC): This phenotype will be assessed by (1) Host-cell reactivation (HCR) assay to measure the host cell's ability to remove adducts in plasmid DNA (a reporter gene) induced by benzo-a-pyrene diol epoxide (BPDE); (2) In vitro induced DNA adduct assay to measure the levels of BPDE-induced adducts in genomic DNA; and (3) Mutagen sensitivity assay to measure the frequency of BPDE-induced chromosomal aberrations. These three phenotypic assays newly developed in our laboratory will be performed using peripheral lymphocytes from 500 cases and 500 controls to assess genetic susceptibility to SCCHN. B. Genetic polymorphisms of metabolic and DNA repair genes: Genotypes of GSTMI, GSTTI, GSTPI, ADH3, XPD, XPC and XRCCI will be determined in 800 cases and 800 controls using genomic DNA by polymerase chain reaction (PCR)-based techniques. As a result, the DNA repair phenotype and genotype correlation will be estimated (in 500 cases and 500 controls). Aim 3: To determine the modification/joint effects and/or gene-environment interactions between exposure to tobacco/alcohol and genotypes of select genes in SCCHN. We will test the hypothesis that those individuals who have both the exposure and an adverse genotype are at elevated risk of developing SCCHN. This aim will be accomplished with 800 cases and 800 controls. We believe this study will advance our knowledge of genetic susceptibility to SCCHN and that these biomarkers for genetic susceptibility will eventually help identify individuals at high risk of developing tobacco/alcohol-related cancer, who could then be targeted for cancer prevention programs, including primary prevention and clinical chemoprevention for second primary cancers.